Three-dimensional printing methods are known in the art and have been successfully used to rapidly construct buildings. For example, Behrokh Khoshnevis of the University of Southern California Information Sciences Institute (in the Viterbi School of Engineering) has developed a printing method that uses a computer-controlled crane or gantry to rapidly construct buildings by deposition of printed cement paste layers. NASA has evaluated this technology for the construction of structures that can be constructed primarily from lunar material.
Current three dimensional printing methods known in the art for rapid construction of buildings utilize computer-controlled gantry systems which move a print head back and forth to fabricate buildings layer by layer. For example, U.S. Pat. No. 7,641,461 disclosed an invention which utilized movement of a print head while discharging printing layers to fabricate a structure. U.S. Pat. No. 8,029,710 further disclosed an invention which utilized a moveable print head to fabricate a structure.
Unfortunately, the above three dimensional printing systems cannot fully utilize advances in printing materials, such as the use of concrete. Concrete is a material that does not have a uniform consistency and which derives its strength, in part, from stones and other aggregate material. Existing spray systems for printing materials are easily clogged because they were designed for discharging a paste having a uniform consistency, such as cement paste.
These systems use a nozzle with an internal valve structure to control the flow of cement paste through an aperture for deposit. However, this valve can easily clog when using material which contains aggregate, such as concrete. Merely increasing the valve and aperture size would require a higher velocity flow and greater pumping volume. The increased volume and rate of flow make it difficult to control and precisely distribute material, thus increasing waste and loss of precision in the fabrication process. This also requires increased size and weight of actuators to move the system, which in turn reduces the system's ability to accurately position the nozzle.
The higher pressures required to expel concrete, as opposed to cement paste, can also damage these print heads and their connected hoses. Furthermore, uncontrolled movement of the heavy delivery hose can cause damage to the printed structure, or cause the hose to detach from the print head, requiring extensive cleanup and repair. This may also decrease printing accuracy due to forces exerted on various parts of the system, which can pull them out of alignment.
There is an unmet need for three dimensional printing systems for buildings which can successfully accommodate the consistency of concrete without compromising the level of precision that can be achieved in the fabrication process.